Pickling of metals



Patented Aug. 8, 195

PICKLING OF METALS Richard 0. Zerbe, Nitro, W. Va., assignor to Monsanto Chemical Company, St. Louis, M0,, a corporation of Delaware No Drawing. Application July 2, 1947, Serial N0. 758,729

18 Claims.

The present invention relates to the cleaning of metallic surfaces and particularly to a new class of steel pickling inhibitors which are employed to prevent undue attack upon the surface of a metal when in contact with a pickling bath of an acid nature.

Pickling solutions for removing oxides from the surface of metals ordinarily consist largely of a dilute solution of an inorganic acid such as sulfuric or hydrochloric acid. The acid although it dissolves the oxides and scale, also attacks the metal to some extent so that the acid is largely consumed and a certain amount of metal is lost. It also appears that the hydrogen liberated by the action of the acid on the metal has a serious embrittling efiect upon the metal being treated. The escaping hydrogen also carries with it a fine spray of the acid liquor from the pickling bath which produces an atmosphere possessing corrosive properties and one which is injurious to health and damaging to equipment.

By the present invention, these objectionable features of the pickling process are substantially overcome or reduced to a minimum. More specifically, some of the objects of the present invention are to obviate over-pickling, embrittlement and pitting of the articles treated; to minimize the amount of metal lost in pickling; to increase the efiiciency of the pickling operation; to prolong the efiective life of the pickling bath; and particularly to facilitate the pickling operation. Other and further objects of the invention will be apparent from the following description and accompanying examples.

To accomplish to as great an extent as possible the objects set forth in accordance with the present invention, there is added to the pickling bath an inhibitor or regulating agent which acts to restrain the action of the acid from attacking clean metal but assists in removing the rust, scale, and other deposits or in other words the inhibitor causes the acid selectively to remove such materials without appreciably attacking the clean portions of the metal under treatment.

The new class of pickle regulators comprise 2-alkyl-mercaptoarylenethiazoles in which the alkyl group bears a terminal hydroxyl group and preferably contains one or more ether linkages. A general formula for the class of products of this invention is where Ar is an ortho arylene radical, R is an alkylene group and n is an integer.

The new inhibitors may be prepared by introducing into mercaptoarylenethiazoles one or more hydroxy alkyl radicals. Examples of suitable arylene thiazoles from which the new inhibitors may be prepared are Z-mercaptobenzothiazole, 2 mercaptonaphthothiazole, 2 mercapto-4-phenylbenzothiazole, 2-mercaptochlorobenzothiazole, and 2-mercaptotolylthiazole.

Condensation of mercaptoarylenethiazoles may be effected with ethylene oxide, propylene oxide, glycide, epichlorhydrin, glycol, glycerine, polyglycerine, and the like. Two or more of these reactive compounds may also be caused to react consecutively. The condensation is advantageously carried out in the presence of alkaline reacting agents or nickel sulfate as catalysts.

An important attribute of the new inhibitors is their ready solubility in the pickling baths. The problem of dispersing insoluble inhibitors is a troublesome one and the presence of undissolved particles in the cleaning bath frequently results in spotting and staining of the metal pieces. While all of the new inhibitors are at least partially soluble in acid pickling baths, those containing approximately four ether linkages are completely soluble. They produce a clear hazefree pickling bath. In addition, the presence of at least one ether group in the molecule increases the inhibiting strength. Therefore, compounds where n in the foregoing general formula is greater than unity are preferred. Solubility determinations carried out in cold dilute acid with condensation products of mercaptobenzothiazole and ethylene oxide revealed that the solubility in acid gradually increased with increasing values of 11.. Products in which the value of n was approximately 10 or more were completely soluble in cold 2% hydrochloric or sulfuric acid. In general, products in which the value of n is at least 5 but less than 31 are completely soluble in hot pickling baths in the amounts normally used.

It is usually preferred to employ between about one hundredth of one percent and three hundredths of one percent by weight based on the pickling bath. However, the composition, concentration, temperature of operation, and other factors vary with different baths and similarly the optimum concentration of inhibitor will Vary somewhat depending upon the particular conditions employed. The concentration of inhibitor based on the quantity of 100 per cent acid contained in the pickling bath is usually between portarit and highly efiicacious group of inhibitors as in all cases wherein one of the preferred inhibiting compounds was incorporated in the ipickle liquor there resulted a great saving in the loss in weight'of the steel test strips as com- Jpared with that resulting when no inhibitor was employed. I p r Other modes of employing inhibitors of the class hereinbefore set forth in the acid pickling of metals are apparent to those skilled in the art to which the invention pertains.- The products described may be employed in the presence of foaming agents, ionizable substances or other materials ordinarily used. Thus the preferred class of materials may beemployed as the sole inhibitor or they may be employed in conjunction with other materials exhibiting an inhibiting action or with inert fillers, dispersing agents, etc. Other non-oxidizing mineral acids than sulfuric acid may be employed in the pickle bath. Thus hydrochloric acid as well as other inorganic acids may be employed in the pickle bath in conjunction with the preferred class of inhibitors in the manner hereinbefore set forth.

What is claimed is: T

l. A process of pickling a ferrous metal which comprises subjecting the metal to be pickled to the action of a heated nonoxidizing mineral acid solution containing about 0.2 to 0.5 percent by Weight based upon 100 percent acid of a compound of the structure S where Ar is an ortho arylene radical, R is an alkylene radical and n is "an integer greater than one but less than thirty-one.

2, A process of pickling a ferrous metal which comprises subjecting the metal to be pickled to the action of a heated nonoxidizing mineral acid solution containing about 0.2 to 0.5 percent by weight based upon 100 percent acid of a compound of the structure s where Ar is an ortho arylene radical, Ris an alkylene radical of less than four carbon atoms and n is an integer greater than one but less than thirty-one.

3. A- process of pickling a ferrous metal which comprises subjecting the metal to be pickled to the action of a heated nonoxidizing mineral acid solution containing about 0.2 to 0.5 percent by weight based upon 100 percent acid of a compound of the structure N Ar CB-(CsH4O)H s where Ar represents an ortho arylene radical and n is an integer greater than one but less than thirty-one.

4. A process of pickling a ferrous metal which comprises subjecting the metal to be pickled to the action of a heated nonoxidizing mineral acid solution containing about 0.2 to 0.5 percent by weight based upon 100 percent acid of a compound of the structure where n is an integer greater than one but less than thirty-one.

5. A process of pickling a. ferrous metal which comprises subjecting the metal to be pickled to the action of a heated nonoxidizing mineral acid solution containing about 0.2 to 0.5 percent by weight based upon percent acid of a compound of the structure 7 where n is an integer not less than ten but less than thirty-one. Y

7. A process of pickling iron and steel products which comprises subjecting the metal tobe pickled to the action of a heated sulfuric acid solution containing about 0.2 to 0.5 percent by weight based upon l00'percent acid of a compound of the structure where n is an integer greater than five but less than thirty-one.

8. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a heated sulfuric acid solution containing about 0.2 to 0.5 percent by weight based upon 100 percent acid of a compound of the structure where n is approximately ten. 9. A mineral acid pickling bath for me products which comprises a nonoxidizing mineral acid solution containin a small proportion suflicient to inhibit the action of the acid On ferrous metals of a compound of the structure.

where Ar is an ortho arylene radical, R is an alkylene radical and n is an integer greater than one but less than thirty-one.

10. A mineral acid pickling bath for metal products which comprises a nonoxidizing mineral acid solution containing a small proportion sufficient to inhibit the action of the acid on ferrous metals of a compound of the structure whene'm: is anfortho arylenez' radical; R is; an alkylene radical of less than four atoms andi-n is an integer greater: than. one: but less thanthirty-one; c r V mineral-s. acid. pickling: bath. for metalnrodncts; which comprises a nonoxidizin-g min.- eraib. acici solution, containing a: small, proportion sufficient to inhibit the action of the acid on ferrous metals of a, compound of the structure N "Ar o'--s csnioxnn I where Ar'oepresents an OBthOe arylene. radical and n is in integer greater than one less than thirty-one. a 12-; A mineral acid pickling bath for metal products which comprises anonoxidizing' min-- eral acid solution containing a small proportion sufilcient to inhibit the action of the acid: on ferrous metals of a componnd of: the structure wheren is: an integer greater than one but. less than thirty-one. 7 V

;.1'3-; A. mineral acid, pickling bath: formetal nmducts comprises a. nonoxidizing mineral acid solution, containing: a small proportion s ufiieient tov inhibit the actionv of: the ,acipi on tel-trolls metals ofla compound of the'structnre where n is an integer not less than ten but less than thirty-one, v V

15. A mineral acid. pickling bath for metal products which. comprises a sulfuric acid solution containing a small proportionsufiicient to mmmmne actifim" or; theacid on ferrous metals or aucomnound oi the structure so. I o-se-ecimoatn s csfplnionn where 'n is approximately ten.

17; A, process of. pickling, iron andv steel proclucts. which comprises. subiecting, the, metal, to be pickled to the action of a. heated; hydrochloric acid solution containing about 02 to 0.57 percent by weight based upon 100 percent. acid of a compound of, the structure where n is an integer greater than five but less than thirty-one.

RICHARD 0. ZERBE.

REFERENCES CITED Thefiollowing. references are of record in the file of this, patent; V

u "ED sTAsrEs, rem TS- Number Name 7 Date 990,963" Tep1pemaL-- Feb; 12', 1935 2383681 Pinkneyet a1 Aug. 28', 1945 

1. PROCESS OF PICKLING A FERROUS METAL WHICH COMPRISES SUBJECTING THE METAL TO BE PICKLED TO THE ACTION OF A HEATED NONOXIDIZING MINERAL ACID SOLUTION CONTAINING ABOUT 0.2 TO 0.5 PERCENT BY WEIGHT BASED UPON 100 PERCENT ACID OF A COMPOUND OF THE STRUCTURE 